REDWOOD CITY -- Four people were badly injured Monday afternoon in a two-car collision on Skyline Boulevard at Alpine Road that shut the roadway for about two hours, according to the California Highway Patrol.

The crash happened shortly before 3 p.m. and involved a Toyota Prius and a second sedan. Four people were taken to Stanford Hospital with major injuries, with one of them taken by helicopter, according to the CHP.

Both lanes were blocked and a sig alert was announced for the area until the roadway was cleared around 4:40 p.m.

No details of what may have caused the crash were available Monday evening.

Contact Eric Kurhi at 408-920-5852. Follow him at Twitter.com/erickurhi.